1. Field of the Invention
The present invention relates to lithographic systems, and more particularly to interferometric lithographic systems with adjustable resolution.
2. Related Art
In interferometric lithographic systems, a laser beam is sent into a beam splitter, the beam splitter divides the laser beam, and then the laser beam is recombined at a substrate that is being exposed, to form a pattern. Typically the patterns being formed involve lines, or rulings, which are used to test such components as photoresist, etc.
Thus, in an interferometric lithographic system, two laser beams are coherently matched, to form fringes at the substrate plane. The fringe pattern exposes the photoresist, which forms a type of a grating pattern. Different interferometric lithographic systems have different ways of generating the two laser beams that will ultimately produce the interference fringes at the substrate.
In conventional interferometric lithographic systems, in order to change the resolution of the system, it is generally necessary to change a number of parameters of the optical system. Typically, this involves replacing some elements of the optics modules. This procedure can be time consuming. Additionally, replacing optical elements or components frequently requires realignment of the components, further increasing the time that the procedure requires.
For example, one of the parameters that needs to change in order to change the resolution of the system is the angle at which the laser beams strike the substrate. This may be viewed as analogous to changing the numerical aperture of the optical system (although, since lenses are not involved in formation of the image in interferometric systems, the numerical aperture at issue is more of a derivative concept).
Other parameters that may need to be changed involve how the beams are separated, and the alignment of various optical components needed to produce the interference fringes. Because of the relatively small coherence length of the laser, there is generally little room for the optical designer to work with, in making sure that the two laser beams actually form the required fringes. In other words, the alignments have to be exact, which is often very difficult to achieve in practical systems, particularly where optical components have to be swapped in and out of the system.
Having changeable optical elements drives the system complexity and cost upward. Each time a user has to change a beam splitter or a optical module, there is risk of losing critical alignments.
Accordingly, there is a need in the art for a system with adjustable resolution and without the alignment complexities of the conventional interferometric lithographic systems.